Java tutorial
/* * Copyright (C) 2014 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.example.android.mediabrowserservice.model; import android.media.MediaMetadata; import android.os.AsyncTask; import com.example.android.mediabrowserservice.utils.LogHelper; import org.json.JSONArray; import org.json.JSONException; import org.json.JSONObject; import java.io.BufferedInputStream; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStream; import java.io.InputStreamReader; import java.net.URL; import java.net.URLConnection; import java.util.ArrayList; import java.util.Collections; import java.util.List; import java.util.Set; import java.util.concurrent.ConcurrentHashMap; import java.util.concurrent.ConcurrentMap; /** * Utility class to get a list of MusicTrack's based on a server-side JSON * configuration. */ public class MusicProvider { private static final String TAG = LogHelper.makeLogTag(MusicProvider.class); private static final String CATALOG_URL = "http://storage.googleapis.com/automotive-media/music.json"; public static final String CUSTOM_METADATA_TRACK_SOURCE = "__SOURCE__"; private static final String JSON_MUSIC = "music"; private static final String JSON_TITLE = "title"; private static final String JSON_ALBUM = "album"; private static final String JSON_ARTIST = "artist"; private static final String JSON_GENRE = "genre"; private static final String JSON_SOURCE = "source"; private static final String JSON_IMAGE = "image"; private static final String JSON_TRACK_NUMBER = "trackNumber"; private static final String JSON_TOTAL_TRACK_COUNT = "totalTrackCount"; private static final String JSON_DURATION = "duration"; // Categorized caches for music track data: private ConcurrentMap<String, List<MediaMetadata>> mMusicListByGenre; private final ConcurrentMap<String, MutableMediaMetadata> mMusicListById; private final Set<String> mFavoriteTracks; enum State { NON_INITIALIZED, INITIALIZING, INITIALIZED } private volatile State mCurrentState = State.NON_INITIALIZED; public interface Callback { void onMusicCatalogReady(boolean success); } public MusicProvider() { mMusicListByGenre = new ConcurrentHashMap<>(); mMusicListById = new ConcurrentHashMap<>(); mFavoriteTracks = Collections.newSetFromMap(new ConcurrentHashMap<String, Boolean>()); } /** * Get an iterator over the list of genres * * @return genres */ public Iterable<String> getGenres() { if (mCurrentState != State.INITIALIZED) { return Collections.emptyList(); } return mMusicListByGenre.keySet(); } /** * Get music tracks of the given genre * */ public Iterable<MediaMetadata> getMusicsByGenre(String genre) { if (mCurrentState != State.INITIALIZED || !mMusicListByGenre.containsKey(genre)) { return Collections.emptyList(); } return mMusicListByGenre.get(genre); } /** * Very basic implementation of a search that filter music tracks which title containing * the given query. * */ public Iterable<MediaMetadata> searchMusic(String titleQuery) { if (mCurrentState != State.INITIALIZED) { return Collections.emptyList(); } ArrayList<MediaMetadata> result = new ArrayList<>(); titleQuery = titleQuery.toLowerCase(); for (MutableMediaMetadata track : mMusicListById.values()) { if (track.metadata.getString(MediaMetadata.METADATA_KEY_TITLE).toLowerCase().contains(titleQuery)) { result.add(track.metadata); } } return result; } /** * Return the MediaMetadata for the given musicID. * * @param musicId The unique, non-hierarchical music ID. */ public MediaMetadata getMusic(String musicId) { return mMusicListById.containsKey(musicId) ? mMusicListById.get(musicId).metadata : null; } public synchronized void updateMusic(String musicId, MediaMetadata metadata) { MutableMediaMetadata track = mMusicListById.get(musicId); if (track == null) { return; } String oldGenre = track.metadata.getString(MediaMetadata.METADATA_KEY_GENRE); String newGenre = metadata.getString(MediaMetadata.METADATA_KEY_GENRE); track.metadata = metadata; // if genre has changed, we need to rebuild the list by genre if (!oldGenre.equals(newGenre)) { buildListsByGenre(); } } public void setFavorite(String musicId, boolean favorite) { if (favorite) { mFavoriteTracks.add(musicId); } else { mFavoriteTracks.remove(musicId); } } public boolean isFavorite(String musicId) { return mFavoriteTracks.contains(musicId); } public boolean isInitialized() { return mCurrentState == State.INITIALIZED; } /** * Get the list of music tracks from a server and caches the track information * for future reference, keying tracks by musicId and grouping by genre. */ public void retrieveMediaAsync(final Callback callback) { LogHelper.d(TAG, "retrieveMediaAsync called"); if (mCurrentState == State.INITIALIZED) { // Nothing to do, execute callback immediately callback.onMusicCatalogReady(true); return; } // Asynchronously load the music catalog in a separate thread new AsyncTask<Void, Void, State>() { @Override protected State doInBackground(Void... params) { retrieveMedia(); return mCurrentState; } @Override protected void onPostExecute(State current) { if (callback != null) { callback.onMusicCatalogReady(current == State.INITIALIZED); } } }.execute(); } private synchronized void buildListsByGenre() { ConcurrentMap<String, List<MediaMetadata>> newMusicListByGenre = new ConcurrentHashMap<>(); for (MutableMediaMetadata m : mMusicListById.values()) { String genre = m.metadata.getString(MediaMetadata.METADATA_KEY_GENRE); List<MediaMetadata> list = newMusicListByGenre.get(genre); if (list == null) { list = new ArrayList<>(); newMusicListByGenre.put(genre, list); } list.add(m.metadata); } mMusicListByGenre = newMusicListByGenre; } private synchronized void retrieveMedia() { try { if (mCurrentState == State.NON_INITIALIZED) { mCurrentState = State.INITIALIZING; int slashPos = CATALOG_URL.lastIndexOf('/'); String path = CATALOG_URL.substring(0, slashPos + 1); JSONObject jsonObj = fetchJSONFromUrl(CATALOG_URL); if (jsonObj == null) { return; } JSONArray tracks = jsonObj.getJSONArray(JSON_MUSIC); if (tracks != null) { for (int j = 0; j < tracks.length(); j++) { MediaMetadata item = buildFromJSON(tracks.getJSONObject(j), path); String musicId = item.getString(MediaMetadata.METADATA_KEY_MEDIA_ID); mMusicListById.put(musicId, new MutableMediaMetadata(musicId, item)); } buildListsByGenre(); } mCurrentState = State.INITIALIZED; } } catch (JSONException e) { LogHelper.e(TAG, e, "Could not retrieve music list"); } finally { if (mCurrentState != State.INITIALIZED) { // Something bad happened, so we reset state to NON_INITIALIZED to allow // retries (eg if the network connection is temporary unavailable) mCurrentState = State.NON_INITIALIZED; } } } private MediaMetadata buildFromJSON(JSONObject json, String basePath) throws JSONException { String title = json.getString(JSON_TITLE); String album = json.getString(JSON_ALBUM); String artist = json.getString(JSON_ARTIST); String genre = json.getString(JSON_GENRE); String source = json.getString(JSON_SOURCE); String iconUrl = json.getString(JSON_IMAGE); int trackNumber = json.getInt(JSON_TRACK_NUMBER); int totalTrackCount = json.getInt(JSON_TOTAL_TRACK_COUNT); int duration = json.getInt(JSON_DURATION) * 1000; // ms LogHelper.d(TAG, "Found music track: ", json); // Media is stored relative to JSON file if (!source.startsWith("http")) { source = basePath + source; } if (!iconUrl.startsWith("http")) { iconUrl = basePath + iconUrl; } // Since we don't have a unique ID in the server, we fake one using the hashcode of // the music source. In a real world app, this could come from the server. String id = String.valueOf(source.hashCode()); // Adding the music source to the MediaMetadata (and consequently using it in the // mediaSession.setMetadata) is not a good idea for a real world music app, because // the session metadata can be accessed by notification listeners. This is done in this // sample for convenience only. return new MediaMetadata.Builder().putString(MediaMetadata.METADATA_KEY_MEDIA_ID, id) .putString(CUSTOM_METADATA_TRACK_SOURCE, source).putString(MediaMetadata.METADATA_KEY_ALBUM, album) .putString(MediaMetadata.METADATA_KEY_ARTIST, artist) .putLong(MediaMetadata.METADATA_KEY_DURATION, duration) .putString(MediaMetadata.METADATA_KEY_GENRE, genre) .putString(MediaMetadata.METADATA_KEY_ALBUM_ART_URI, iconUrl) .putString(MediaMetadata.METADATA_KEY_TITLE, title) .putLong(MediaMetadata.METADATA_KEY_TRACK_NUMBER, trackNumber) .putLong(MediaMetadata.METADATA_KEY_NUM_TRACKS, totalTrackCount).build(); } /** * Download a JSON file from a server, parse the content and return the JSON * object. * * @return result JSONObject containing the parsed representation. */ private JSONObject fetchJSONFromUrl(String urlString) { InputStream is = null; try { URL url = new URL(urlString); URLConnection urlConnection = url.openConnection(); is = new BufferedInputStream(urlConnection.getInputStream()); BufferedReader reader = new BufferedReader( new InputStreamReader(urlConnection.getInputStream(), "iso-8859-1")); StringBuilder sb = new StringBuilder(); String line; while ((line = reader.readLine()) != null) { sb.append(line); } return new JSONObject(sb.toString()); } catch (Exception e) { LogHelper.e(TAG, "Failed to parse the json for media list", e); return null; } finally { if (is != null) { try { is.close(); } catch (IOException e) { // ignore } } } } }